The incident is regarded as terrorist-related, London Metropolitan Police said. It added on its Facebook site that London Ambulance reported 18 people were hospitalized.

Passengers said a wall of fire could be seen and felt aboard one car on the train.

Witnesses said several people were seen with severe burns, and others who were injured as passengers hurried to leave the train. Police have not issued a casualty count.

None of the injuries are life-threatening, officials said.

The incident prompted panic in the subway — which is the world’s oldest and among busiest — disrupted schedules and drew a quick and heavy response from rescue workers and armed police.

Friday’s fire was the fifth terrorism-related attack in London in 2017. The previous four killed 36 people, and police said six other significant plots, soon to be prosecuted, were thwarted before they occurred.

In early morning Twitter comments, President Donald Trump said, “Another attack in London by a loser terrorist.These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”

Minutes later he said, “Loser terrorists must be dealt with in a much tougher manner.The internet is their main recruitment tool which we must cut off & use better!”